Alkaline storage batteries including a negative electrode which includes a hydrogen storage alloy as a negative electrode active material are excellent in output characteristics, and have excellent durability (e.g., life characteristics and/or storage characteristics). Such alkaline storage batteries are attracting attention for use as a replacement for dry batteries, a driving power source for electric vehicles, and other applications. On the other hand, lithium ion secondary batteries are also increasingly used for these applications in recent years. In view of increasing the advantage of alkaline storage batteries, the battery characteristics including output characteristics and durability are expected to be further improved.
The most widely used hydrogen storage alloy is the one having a CaCu5-type crystal structure. To improve the battery characteristics of alkaline storage batteries, various attempts have been made to optimize the performance of the hydrogen storage alloy powder.
For example, Patent Literature 1 proposes that, in view of improving the storage characteristics at high temperatures, a hydrogen storage alloy containing La-mischmetal (La content: 60 to 90 wt %), Ni, Co and Mn, and Mg and being surface-treated with acid or alkali be used as a negative electrode active material for alkaline storage batteries.
Patent Literature 2 proposes that, in view of improving the battery capacity and the high rate discharge characteristics as well as suppressing crumbling into fine powder, a hydrogen storage alloy having a CaCu5-type crystal structure and containing 24 to 33 wt % of La and 0.1 to 1.0 wt % of Mg or Ca be used as a negative electrode active material for nickel-metal hydride storage batteries.
Patent Literature 3 proposes that, in view of improving the cycle characteristics and discharge capacity, a hydrogen storage alloy having a CaCu5-type crystal structure and containing: rare earth element A including Y; Mg and/or Ca; an element such as Co, Mn and Al; and Ni be used as an electrode active material for nickel-metal hydride storage batteries.